The present invention relates to apparatus for the simultaneous photometric determination of a plurality of elements in a liquid sample, in which apparatus a receiver is associated with each of the elements to be determined and the signals supplied by said receivers are evaluated via a computer.
The liquid sample under examination may, for instance, be a body fluid, such as serum, urine, spinal fluid, etc., the purpose generally being to determine the content of sodium, potassium, calcium and frequently also, magnesium in the sample.
A flame photometer for the simultaneous determination of sodium and potassium in a sample dilution is already known. However, calcium, which is important for diagnosis, and furthermore magnesium, which is important, for instance, for dialysis centers, cannot be determined with the known device.
It is also known to determine the elements sodium, potassium, and calcium one after the other by means of a flame photometer. In this case, however, different dilutions are needed, so that the time required for the measurement, and the amount of sample needed are relatively great. Here again, the measurement of magnesium is not possible, and the determination of calcium is subject to error.
Finally, it is also known to determine sodium and potassium one after the other through flame emission, and calcium and magnesium one after the other through atomic absorption. Aside from the fact that instruments for such determinations are expensive and make high demands on the operator, the time and the quantity of sample required for a measurement of the said elements are rather great.
The foregoing shortcomings are due, in particular, to the fact that so-called comparison elements are necessary, which form an internal standard by means of which it is possible to eliminate variations in measurement values. A comparison element is added to the sample, has the same energy of excitation as the element being analyzed, and is measured simultaneously with the latter in the same section of the flame. For sodium and potassium, lithium is customarily used as the comparison element in emission photometry. For the analysis of calcium by atomic absorption, strontium is suitable as the comparison element; and for the analysis of magnesium, cadmium is suitable.
It is clear that when determining four elements, the time and sample quantity required for a measurement, as well as the equipment expense for the preparation of the sample, are all rather high. Furthermore, undesired or even disturbing effects of the addition of such comparison elements are likely if the necessary measurement conditions are not precisely satisfied.